According to the invention there is provided a balloon catheter comprising an elongated catheter extending between a proximal end and a distal end, an inflatable element defining a hollow interior region located on the catheter, a first lumen extending along the catheter from the proximal end to the inflatable element communicating with the inflatable element for accommodating an inflating medium to the inflatable element, a pressure sensing element communicating with the hollow interior region of the inflatable element for sensing pressure of an inflating medium in the inflatable element, the pressure sensing element being located in a chamber formed in a protective housing located adjacent the inflatable element, the protective housing having a communicating opening communicating the pressure sensing element with the hollow interior region of the inflatable element.
In one embodiment of the invention the protective housing comprises a non-deformable housing.
Preferably, the protective housing is located within the catheter. Advantageously, the protective housing is located within a cavity formed in the catheter, the chamber of the protective housing communicating with the cavity through the communicating opening. Preferably, the cavity in the catheter communicates with the hollow interior region of the inflatable element. Ideally, the cavity, within which the protective housing is located, is located in the catheter within the inflatable element.
In one embodiment of the invention the catheter extends through the inflatable element, and the inflatable element defines with the catheter the hollow interior region as an annular hollow interior region.
In another embodiment of the invention the protective housing comprises an elongated tubular housing. Preferably, the tubular housing terminates in one end in the communicating opening for communicating with the hollow interior region of the inflatable element. Advantageously, the protective housing is of circular transverse cross-section.
In one embodiment of the invention a tubular port extends from the protective housing.
In another embodiment of the invention the tubular port forms the communicating opening.
Preferably, the tubular port extends from the protective housing at an end opposite to the end which terminates in the communicating opening.
Advantageously, the tubular port is adapted for accommodating at least one electrically conductive wire to the pressure sensing element. Preferably, the at least one electrically conductive wire is secured to the protective housing. Advantageously, the at least one electrically conductive wire is secured to the protective housing by an adhesive. Ideally, the at least one electrically conductive wire is secured to the protective housing in the chamber.
In one embodiment of the invention the at least one electrically conductive wire is secured to the protective housing in the tubular port. Alternatively, the at least one electrically conductive wire extends to the pressure sensing element from the proximal end of the catheter.
In another embodiment of the invention the pressure sensing element is located in the chamber to be free floating therein.
In another embodiment of the invention the pressure sensing element comprises a solid state strain gauge.
In a further embodiment of the invention the inflatable element is located on the catheter adjacent the distal end thereof. Preferably, the first lumen extends through the catheter from the proximal end thereof to the inflatable element.
In one embodiment of the invention a measuring means is provided for determining a transverse cross-sectional dimension of the inflatable element. Preferably, the measuring means is located within the inflatable element for measuring a value of a transverse cross-sectional dimension of the inflatable element.
In one embodiment of the invention the measuring means comprises at least one stimulating electrode located within the inflatable element on one of the catheter and the inflatable element for receiving an electrical stimulating signal, and at least one sensing electrode located within the inflatable element on one of the catheter and the inflatable element axially spaced apart from the stimulating electrode, the at least one sensing electrode being responsive to a stimulating signal applied to the at least one stimulating electrode when the inflatable element is inflated with an electrically conductive medium for producing a response signal indicative of a value of the transverse cross-sectional dimension of the inflatable element adjacent the sensing electrode.
Advantageously, a pair of axially spaced apart stimulating electrodes are provided. Preferably, a plurality of axially spaced apart sensing electrodes are provided between the two stimulating electrodes and axially spaced apart therefrom.
In one embodiment of the invention the axial spacing between at least two of the sensing electrodes is greater than the axial spacing between others of the sensing electrodes to increase the sensitivity with which the value of transverse cross-sectional dimension of the inflatable element is determined.
In another embodiment of the invention the axial spacing between the sensing electrodes is greatest at a location where the transverse cross-section of the inflatable element is adapted to be greatest.
In a further embodiment of the invention the axial spacing between the sensing electrodes is greatest at a location where the transverse cross-sectional area of the inflatable element is greatest when in use.
In a further embodiment of the invention the sensing electrodes between which the axial spacing is greatest are located at a position intermediate the axial opposite ends of the hollow interior region of the inflatable element. Alternatively, the sensing electrodes between which the axial spacing is greatest are located adjacent the axial centre of the hollow interior region of the inflatable element.
In another embodiment of the invention the sensing electrodes between which the axial spacing is greatest are located towards at least one axial end of the hollow interior region of the inflatable element.
In a further embodiment of the invention the sensing electrodes between which the axial spacing is greatest are located towards respective axial opposite ends of the inflatable element.
In a further embodiment of the invention the inflatable element when inflated is adapted to be of stepped transverse cross-section, and the sensing electrodes between which the axial spacing is greatest are located adjacent the portion of the inflatable element adapted to be of greatest transverse cross-section when inflated, and the sensing electrodes between which the axial spacing is least are located adjacent the portion of the inflatable element adapted to be of smallest transverse cross-section when inflated.
In another embodiment of the invention the axial spacing between at least three of the sensing electrodes of greatest axial spacing is substantially similar.
Preferably, the axial spacing between at least five of the sensing electrodes of greatest axial spacing is substantially similar.
Advantageously, the axial spacing between the sensing electrodes progressively decreases from the sensing electrodes of greatest axial spacing therebetween to the sensing electrodes of least axial spacing therebetween.
In one embodiment of the invention the greatest axial spacing between the sensing electrodes lies in the range of 5 mm to 10 mm. Preferably, the minimum axial spacing between the sensing electrodes lies in the range of 2 mm to 5 mm.
Preferably, each stimulating electrode is located on the catheter. Advantageously, each sensing electrode is located on the catheter. Preferably, each stimulating electrode comprises a band electrode extending around the catheter. Advantageously, each sensing electrode comprises a band electrode extending around the catheter. Ideally, each band electrode extends completely around the catheter.
In one embodiment of the invention a communicating means is provided for communicating each stimulating electrode with a signal generator remote from the hollow interior region of the inflatable element, and for communicating each sensing electrode with a signal processing means remote of the hollow interior region of the inflatable element.
Preferably, the communicating means comprises a plurality of mutually insulated electrically conductive wires extending from the respective stimulating and sensing electrodes.
Advantageously, a second lumen is provided extending along the catheter from the proximal end thereof to the electrodes for accommodating the wires from the respective electrodes to the proximal end of the second lumen. Preferably, the second lumen extends through the catheter.
In one embodiment of the invention a portion of the second lumen adjacent the inflatable element forms the cavity within which the protective housing is located. Preferably, the electrically conductive wires extending from the pressure sensing element through the protective housing are accommodated through the second lumen to the proximal end of the catheter.
In another embodiment of the invention a temperature sensing means is provided for monitoring the temperature of the pressure sensing element. Preferably, the temperature sensing means is adapted for monitoring the temperature of the inflating medium for facilitating compensating for temperature variation of the pressure sensing element during reading of signals from the pressure sensing element indicative of the pressure of the inflating medium. Advantageously, the temperature sensing means is adapted for monitoring the temperature of the inflating medium for facilitating compensating for temperature variation of the inflating medium when reading signals from the sensing electrodes indicative of the transverse cross-sectional dimension of the inflatable element adjacent the respective sensing electrodes.
In one embodiment of the invention an isolating means is located in the second lumen intermediate the proximal end thereof and the inflatable element for preventing inflating medium exiting through the proximal end of the second lumen.
In another embodiment of the invention a guide wire accommodating lumen extends internally through the catheter.
In an alternative embodiment of the invention a guide wire engaging means is mounted externally on one of the catheter and the inflatable element for engaging a guide wire for guiding of the balloon catheter along the guide wire to a remote site. Preferably, the guide wire engaging means comprises a guide wire engaging element extending from the one of the catheter and the inflatable element. Advantageously, the guide wire engaging element defines a guide wire accommodating opening for slideably accommodating the guide wire therethrough. Ideally, the guide wire accommodating opening is provided by a guide wire accommodating bore extending through the guide wire engaging element. Preferably, the guide wire accommodating bore is sized to form a sliding fit on the guide wire. Advantageously, the guide wire accommodating bore defines a central axis extending parallel to the catheter.
In one embodiment of the invention the guide wire engaging means is mounted on the catheter and extends transversely thereof. Preferably, the guide wire engaging means is located adjacent the distal end of the catheter.
In another embodiment of the invention a plurality of guide wire engaging means are located axially spaced apart along a portion of the catheter. Preferably, the guide wire engaging means are located axially spaced apart along substantially the length of the catheter.
Advantageously, the guide wire engaging means is releasably mounted on the balloon catheter.
In another embodiment of the invention the guide wire engaging means comprises a lumen extending along a portion of the catheter externally thereof.
In a further embodiment of the invention the guide wire engaging means is mounted on the inflatable element.
In one embodiment of the invention the inflatable element comprises a balloon.
The invention also provides in combination a balloon catheter according to the invention and a guide wire engaged in the guide wire engaging means.
The invention further provides a balloon catheter comprising an elongated catheter extending between a proximal end and a distal end, and an inflatable element defining a hollow interior region located on the catheter, a first communicating means for accommodating an inflating medium to the hollow interior region of the inflatable element, a plurality of axially spaced apart measuring electrodes located within the hollow interior region of the inflatable element on one of the catheter and the inflatable element, at least one of the measuring electrodes being a stimulating electrode for receiving a stimulating signal, and a plurality of the measuring electrodes being sensing electrodes, the sensing electrodes being responsive to a stimulating signal being applied to the at least one stimulating electrode when the inflatable element is inflated with an electrically conductive inflating medium for producing response signals indicative of values of a transverse cross-sectional dimension of the inflatable element adjacent the corresponding sensing electrodes, the axial spacing between at least two of the sensing electrodes being greater than the axial spacing between others of the sensing electrodes to increase the sensitivity with which the value of transverse cross-sectional dimension of the inflatable element is determined.
Preferably, the axial spacing between the sensing electrodes is greatest at a location where the transverse cross-section of the inflatable element is adapted to be greatest.
Advantageously, the axial spacing between the sensing electrodes is greatest at a location where the transverse cross-section of the inflatable element is greatest when in use.
The invention also provides a catheter comprising an externally located guide wire engaging means adapted for engaging a guide wire for guiding of the catheter along the guide wire.
Preferably, the guide wire engaging means is adapted to slideably engage the guide wire. Advantageously, the guide wire engaging means comprises a guide wire engaging element extending from the catheter. Preferably, the guide wire engaging element defines a guide wire accommodating opening for slideably accommodating the guide wire therethrough.
Further the invention provides a device for mounting on a catheter externally of the catheter, the device comprising a guide wire engaging means adapted for engaging a guide wire externally of the catheter for guiding of the catheter along the guide wire.
Preferably, the guide wire engaging means is adapted for slideably engaging the guide wire.
Ideally, the device is adapted for releasably engaging the catheter.
The invention also provides a method for accessing a remote site in a body of a human or animal by a catheter, the method comprising passing a guide wire through a lumen, a vessel or a vascular system in the body to the remote site, providing a catheter with an externally located guide wire engaging means mounted on the catheter, engaging the guide wire engaging means with the guide wire, and urging the catheter with the guide wire engaging means engaged on the guide wire along the guide wire through the lumen, vessel or vascular system in the body to the remote site.
Further the invention provides a method for increasing the sensitivity with which a value of a transverse cross-sectional dimension of an inflatable element of a balloon catheter is determined, wherein the balloon catheter comprises an elongated catheter extending between a proximal end and a distal end, and the inflatable element defining a hollow interior region is located on the catheter, a first communicating means being provided for accommodating an inflating medium to the hollow interior region of the inflatable element, a plurality of axially spaced apart measuring electrodes located within the hollow interior region of the inflatable element on one of the catheter and the inflatable element, at least one of the measuring electrodes being a stimulating electrode for receiving a stimulating signal, and a plurality of the measuring electrodes being sensing electrodes on which respective response signals are produced indicative of the value of a transverse cross-sectional dimension of the inflatable element adjacent the corresponding sensing electrodes in response to a stimulating signal being applied to the at least one stimulating electrode when the inflatable element is inflated with an electrically conductive inflating medium, the method comprising providing at least two of the sensing electrodes adjacent a location at which the transverse cross-section of the inflatable element is to be greatest in use, with an axial spacing therebetween greater than the axial spacing between others of the sensing electrodes to thereby increase the sensitivity with which the value of the transverse cross-sectional dimension of the inflatable element is determined adjacent the at least two of the sensing electrodes of the greatest spacing therebetween.
Additionally, the invention provides a method for increasing the accuracy with which the pressure of inflating medium in an inflatable element mounted on a catheter of a balloon catheter is determined, wherein the catheter comprises an elongated catheter extending between a proximal end and a distal end, the inflatable element defining a hollow interior region is located on the catheter, and a first lumen extending along the catheter from the proximal end to the inflatable element accommodates an inflating medium to the inflatable element, the method comprising locating a pressure sensing element in a chamber formed in a protective housing located adjacent the inflatable element, the protective housing having a communicating opening communicating the pressure sensing element with the hollow interior region of the inflatable element.
The invention further provides a method for forming a stoma of a desired internal transverse cross-section in a hollow vessel, the method comprising providing a balloon catheter comprising an elongated catheter extending between a proximal end and a distal end, an inflatable element defining a hollow interior region located on the catheter, a measuring means for determining a value of a transverse cross-sectional dimension of the inflatable element, the method further comprising locating the inflatable element in the hollow vessel adjacent a location at which the stoma is to be formed, inflating the inflatable element to a degree that the inflatable element bears on the vessel adjacent the location at which the stoma is to be formed, operating the measuring means to determine the value of the transverse cross-sectional dimension of the inflatable element adjacent the location at which the stoma is to be formed, and continuously updating the determined value of the transverse cross-sectional dimension of the inflatable element, placing a band around the exterior of the hollow vessel adjacent the location at which the stoma is to be formed, and one of tightening and loosening the band until the determined value of the transverse cross-sectional dimension of the inflatable element adjacent the stoma corresponds with a desired internal transverse cross-section of the stoma.
In one embodiment of the invention the band is partly tightened to produce the stoma of the appropriate desired internal transverse cross-section prior to inflating of the inflatable element in the vessel.
In another embodiment of the invention the inflatable element is inflated prior to tightening of the band.
In another embodiment of the invention the inflatable element is inflated with a predefined volume of an inflating medium.
In a further embodiment of the invention the inflatable element is inflated to a predefined pressure.
In a still further embodiment of the invention the inflatable element is inflated to the predefined pressure prior to tightening of the band and the band is tightened until the stoma is of a desired internal cross-section corresponding to the predefined pressure to which the inflatable element has been inflated which corresponds to the pressure exerted on the stoma by the inflatable element.
Preferably, the predefined pressure to which the inflatable element is inflated is at least 5 mm of mercury.
Advantageously, the predefined pressure to which the inflatable element is inflated is at least 10 mm of mercury. Ideally, the predefined pressure to which the inflatable element is inflated is at least 15 mm of mercury.
In another embodiment of the invention the measuring means comprises at least one stimulating electrode located within the inflatable element on one of the catheter and the inflatable element, and at least one sensing electrode located within the inflatable element on one of the catheter and the inflatable element axially spaced apart from the stimulating electrode, the method further comprising inflating the inflatable element with an electrically conductive medium, applying a constant current stimulating signal of known value to the at least one stimulating electrode and reading a response signal from the at least one sensing electrode in response to the stimulating signal and determining the value of the transverse cross-sectional dimension of the inflatable element adjacent the at least one sensing electrode from the read response signal.
Preferably, the stimulating signal is applied to the at least one stimulating electrode continuously while the band is being one of tightened and loosened.
Advantageously, the response signal from the at least one sensing electrode is continuously read from the at least one sensing electrode.
In one embodiment of the invention the stimulating signal is applied to the at least one stimulating electrode and the response signal is continuously read from the at least one sensing electrode simultaneously with inflating of the inflatable element.
Advantageously, the stimulating signal is applied to the at least one stimulating electrode and the response signal is read from the at least one sensing electrode simultaneously with tightening of the band around the hollow vessel to form the stoma.
Preferably, the method is adapted for forming a stoma in a stomach of a human or animal body.
In one embodiment of the invention the band is a gastric band comprising an elongated band securable around the stomach, and an inflating cuff extending along the band. Advantageously, the gastric band is secured around the outside of the stomach at a location adjacent to which the stoma is to be formed by the inflatable cuff. Preferably, the gastric band is secured around the outside of the stomach with the inflatable cuff located between the gastric band and the stomach.
In one embodiment of the invention the inflatable cuff is inflated until the internal transverse cross-section of the stoma is of the desired cross-section.
In another embodiment of the invention the transverse cross-sectional dimension of the inflatable element which is determined is one of the diameter and the area of the transverse cross-section of the inflatable element adjacent the stoma.
Preferably, a human sensory perceptible signal indicative of the value of the transverse cross-sectional dimension of the inflatable element is produced from the determined value of the transverse cross-sectional dimension of the inflatable element. Advantageously, the human sensory perceptible signal indicative of the transverse cross-section of the stoma is displayed on a visual display screen. Preferably, the human sensory perceptible signal indicative of the transverse cross-sectional dimension of the inflatable element is displayed in the form of one of an alpha or numeric display. Advantageously, the human sensory perceptible signal indicative of the transverse cross-sectional dimension of the inflatable element is displayed in the form of a graphical representation of a portion of the inflatable element adjacent the stoma.
In one embodiment of the invention the graphical representation is displayed as a two-dimensional longitudinal cross-sectional elevational view of the stoma. Preferably, the graphical representation is displayed as a two-dimensional longitudinal cross-sectional elevational view of the stoma and an adjacent part of the vessel.
In an alternative embodiment of the invention the graphical representation is displayed as a three-dimensional longitudinal view of the stoma and an adjacent portion of the vessel.
The invention also provides a method for monitoring the internal transverse cross-section of a stoma as the stoma is being formed in a vessel, the method comprising providing a balloon catheter comprising an elongated catheter extending between a proximal end and a distal end, an inflatable element defining a hollow interior region located on the catheter, a measuring means for determining a value of a transverse cross-sectional dimension of the inflatable element, locating the inflatable element in the hollow vessel adjacent a location at which the stoma is to be formed, inflating the inflatable element to a degree that the inflatable element bears on the vessel adjacent the location at which the stoma is to be formed, operating the measuring means to determine the value of the transverse cross-sectional dimension of the inflatable element adjacent the location at which the stoma is to be formed, and continuously updating the value of the transverse cross-sectional dimension of the inflatable element adjacent the location at which the stoma is to be formed.
Preferably, the value of the transverse cross-sectional dimension of the inflatable element is displayed, and the displayed value of the transverse cross-sectional dimension of the inflatable element is continuously updated. Advantageously, the pressure of the inflating medium of the inflatable element is monitored during formation of the stoma.
Preferably, the pressure of the inflating medium in the inflatable element is maintained substantially constant during formation of the stoma.
Ideally, the inflating medium in the inflatable element is maintained constant at a predefined pressure during formation of the stoma.
In another embodiment of the invention the predefined pressure to which the inflatable element is inflated is at least 5 mm of mercury. Advantageously, the predefined pressure to which the inflatable element is inflated is at least 10 mm of mercury. Advantageously, the predefined pressure to which the inflatable element is inflated is at least 15 mm of mercury.
The invention also provides apparatus for monitoring the internal transverse cross-section of a stoma in a hollow vessel as the stoma is being formed, the apparatus comprising an elongated catheter extending between a proximal end and a distal end, an inflatable element located on the catheter, the inflatable element being adapted for locating in the vessel adjacent the location at which the stoma is to be formed, a measuring means for determining a value of a transverse cross-sectional dimension of the inflatable element, so that when the inflatable element is located in the vessel adjacent the location at which the stoma is to be formed with the inflatable element inflated to engage the vessel adjacent the location at which the stoma is to be formed, a value of the transverse cross-sectional dimension corresponding to the internal transverse cross-section of the stoma is determined by the measuring means.
In one embodiment of the invention a means is provided for producing a human sensory perceptible signal indicative of the value of the transverse cross-sectional dimension of the inflatable element adjacent the location of the stoma.
Advantageously, a display means is provided for displaying the human sensory perceptible signal indicative of the value of the transverse cross-sectional dimension of the inflatable element adjacent the stoma.
Advantageously, the display means displays the value of the transverse cross-sectional dimension of the inflatable element adjacent the stoma as one of an alpha or a numeric display.
Preferably, the display means displays the transverse cross-section of the inflatable element adjacent the stoma as a graphical representation thereof.
In one embodiment of the invention the graphical representation of the transverse cross-section of the inflatable element adjacent the stoma is a two-dimensional representation of a longitudinal cross-section of the stoma and an adjacent part of the vessel.
In an alternative embodiment of the invention the graphical representation of the value of the transverse cross-section of the inflatable element adjacent the stoma is a three-dimensional graphical representation of a longitudinal cross-section of the stoma and an adjacent part of the vessel.
In another embodiment of the invention the measuring means comprises at least one stimulating electrode located within the inflatable element on one of the catheter and the inflatable element, and at least one sensing electrode located within the inflatable element on one of the catheter and the inflatable element axially spaced apart from the stimulating electrode so that when the inflatable element is inflated with an electrically conductive medium and a constant current signal is applied to the at least one stimulating electrode, a voltage response signal produced on the at least one sensing electrode is indicative of the value of the transverse cross-sectional dimension of the inflatable element adjacent the at least one sensing electrode.
Advantageously, a pressure sensing element is provided for monitoring the pressure of inflating medium in the inflatable element during formation of the stoma.
The invention also provides apparatus for monitoring the internal transverse cross-section of a stoma in a hollow vessel as the stoma is being formed, the apparatus comprising a balloon catheter, the balloon catheter comprising an elongated catheter extending between a proximal end and a distal end, and an inflatable element located on the catheter, the inflatable element being adapted for locating in the hollow vessel adjacent a location at which the stoma is to be formed, at least one stimulating electrode located within the inflatable element on one of the catheter and the inflatable element, and at least one sensing electrode located within the inflatable element axially spaced apart from the stimulating electrode on one of the catheter and the inflatable element, the apparatus further comprising a first inflating means for inflating the inflatable element with an electrically conductive inflating medium to a degree that the inflatable element bears on the vessel adjacent the location at which the stoma is to be formed, a means for applying a current stimulating signal of known value to the at least one stimulating electrode, a means for reading a response signal from the at least one sensing electrode in response to the stimulating signal applied to the at least one stimulating electrode, a means for computing a value of a transverse cross-sectional dimension of the inflatable element adjacent the location at which the stoma is to be formed from the response signal read from the at least one sensing electrode representative of the internal transverse cross-section of the stoma.
Preferably, a means is provided for producing a human sensory perceptible signal indicative of the current value of one of the diameter and the area of the internal transverse cross-section of the location of the vessel at which the stoma is being formed as the stoma is being formed. Preferably, a display means is provided for displaying the value of the one of the diameter and the area of the internal transverse cross-section of the location of the vessel at which the stoma is being formed as the stoma is being formed in one of alpha and numeric characters. Advantageously, the display means is adapted for displaying a graphical representation of the location of the vessel at which the stoma is being formed as the stoma is being formed.
In one embodiment of the invention the graphical representation is a two-dimensional graphical representation. Alternatively, the graphical representation is a three-dimensional representation.
In one embodiment of the invention the apparatus is adapted for producing an alert signal when the value of the one of the diameter and the area of the internal transverse cross-section of the location of the vessel at which the stoma is being formed as the stoma is being formed is equal to a predefined value.
In one embodiment of the invention the apparatus is adapted for monitoring the internal transverse cross-section of a stoma being formed in a stomach, whereby the stoma is being formed by a gastric band having a band for securing around the stomach at a location where the stoma is to be formed, and a means for tightening the band around the stomach to form the stoma, the apparatus further comprising a means for controlling tightening of the gastric band around the stomach, the means for controlling the tightening of the gastric band around the stomach being responsive to the computing means for controlling the tightening of the gastric band to produce the stoma to be of a desired internal transverse cross-section.
Preferably, the means for controlling the tightening of the gastric band is adapted for controlling the tightening of a gastric band of the type comprising a band for locating around the stomach and an inflatable cuff attached to the band for locating between the band and the stomach at the location at which the stoma is to be formed, and the means for controlling the tightening of the gastric band comprises an inflating control means for controlling inflating of the inflatable cuff of the gastric band.
In one embodiment of the invention a volume monitoring means is provided for monitoring the volume of inflating medium in the inflatable cuff of the gastric band.
In another embodiment of the invention a pressure monitoring means is provided for monitoring the pressure of the inflating medium in the inflatable cuff of the gastric band.
Preferably, a means is provided for determining a relationship between change in the internal transverse cross-section of the stoma and change in the tightness of the gastric band.
In one embodiment of the invention the means for determining the relationship between change in the internal transverse cross-section of the stoma and tightness of the gastric band determines the relationship from computed values of the internal transverse cross-section of the stoma computed by the computing means and corresponding tightness values of the gastric band.
Advantageously, the means for determining the relationship between change in the internal transverse cross-section of the stoma and change in the tightness of the band determines the relationship between change in the internal transverse cross-section of the stoma and inflating of the inflatable cuff.
Preferably, the tightness of the gastric band is determined by one of the volume and the pressure of the inflating medium in the inflatable cuff of the gastric band.
Ideally, the means for determining the relationship between change in the internal transverse cross-section of the stoma and change in the tightness of the gastric band determines the change in the internal transverse cross-section of the stoma for each unit of inflating medium delivered into or out of the inflatable cuff of the gastric band.
In one embodiment of the invention the determined relationship between the change in the internal transverse cross-section of the stoma and the tightness of the gastric band is stored in a storing means. Preferably, the relationship between change in the internal transverse cross-section of the stoma and the tightness of the gastric band is stored in the form of a look-up table. Ideally, the look-up table contains values of the internal transverse cross-sectional area or diameter of the stoma against corresponding values of the volume of inflating medium in the inflatable cuff of the gastric band.
In one embodiment of the invention the apparatus is adapted for controlling inflating and deflating of the inflatable cuff of the gastric band to produce the stoma to be of a desired internal transverse cross-section based on the determined relationship between the change in the internal transverse cross-section of the stoma and the tightness of the gastric band.
The advantages of the balloon catheters according to the invention are many. Firstly, the pressure of the inflating medium within the inflatable element of the balloon catheter can be relatively accurately determined. By locating the pressure sensing element within or adjacent the hollow interior region of the inflatable element, the pressure sensing element monitors the pressure of the inflating medium within the hollow interior region of the inflatable element directly, and thus, the pressure of the inflating medium monitored by the pressure sensing element is substantially the true value of the pressure of the inflating medium in the hollow interior region of the inflatable element. By locating the pressure sensing element in the protective housing, the pressure sensing element is decoupled from substantially all and in most cases all pressures and forces other than the pressure of the inflating medium in the hollow interior region of the inflatable element. For example, the protective housing absorbs any pressures which would result from bending, twisting or otherwise deforming the catheter when the protective housing is mounted in or on the catheter. Similarly, when mounted adjacent the inflatable element, the protective housing absorbs any pressures which may be induced therein by pressure of the inflatable element bearing on the protective housing. Thus, the protective housing protects the pressure sensing element from any extrinsic pressures resulting from bending, twisting or otherwise deforming the catheter, and from any such pressures resulting from the inflatable element bearing on the protective housing. Therefore, the signals produced by the pressure sensing element are solely indicative of the pressure of the inflating medium within the hollow interior region of the inflatable element. By providing the protective housing as a non-deformable housing, the pressure sensing element is completely decoupled from all other pressures and forces other than the pressure of the inflating medium within the hollow interior region of the inflatable element.
Secondly, the balloon catheters and the catheters according to the invention are suitable for guiding along an externally located guide wire to a remote site in the body of a human or animal subject.
Thirdly, the sensitivity with which the values of the transverse cross-sectional area or diameter of a vessel of varying transverse cross-sectional area can be determined is significantly improved.
Using the method and apparatus for monitoring the formation of a stoma allows the stoma to be formed more accurately to a desired internal transverse cross-sectional area or diameter, and the method for forming a stoma according to the invention similarly allows the stoma to be formed more accurately to a desired internal transverse cross-sectional area or diameter.
A further advantage of the invention is provided when the apparatus for monitoring the stoma is adapted for determining a relationship between change in the internal cross-section of the stoma and change in the tightness of a gastric band forming the stoma. By determining the said relationship, inflating and deflating of an inflatable cuff of a gastric band used for forming the stoma can be controlled based on the determined relationship between the change in internal transverse cross-section of the stoma and the tightness of the gastric band in order to produce the stoma to a desired internal transverse cross-section.
By storing the determined relationship between the change in the internal transverse cross-section of the stoma and the tightness of the gastric band, subsequent inflation of the gastric band may be controlled based on the said determined relationship for subsequently adjusting the internal transverse cross-section of the stoma without the need to monitor the internal transverse cross-section of the stoma within the stomach. Storing the said determined relationship between change in the internal cross-section of the stoma and the tightness of the gastric band in the form of a look-up table permits both manual and automatic subsequent adjustment of the internal transverse cross-section of the stoma without the need to monitor the internal transverse cross-section of the stoma within the stomach.